This helped me alot, so i'm sure its gonna have an impact on your n900 aswell.

I just hope someone can tell us if its the switching of networks that drains it and not the 3G it self. I'm concidering to switch cell provider over to 3. They only have 3G network in denmark, no gsm... so no network switching. But that wouldn't help much if 3G sucks battery like crazy.